Right angle bending prisms work effectively by total internal reflection. They are anti-reflection coated on the legs. Optionally, the hypotenuse may be coated with second-surface aluminum protected by black sealing paint to ensure grazing incidence reflection. These prisms are suitable for optical delay lines and for high power use. 

Parameter: 

Material: BK7, Fused silica 
Dimension Tolerance: ± 0.10mm
Surface Flatness: λ /8@633nm over clear aperture
Surface quality: 20/10
Angle Tolerance: ± 10arc sec---± 3arc min
Perpendicularity: ± 2arc min
Clear Aperture: 90% of central circular dimension
Bevel: 0.3mmx45°